1. Field of the Invention
The present invention relates to a batch cryogenic freezing apparatus utilizing a cold gas mixture which continually circulates through the freezing chamber. Additional cold gas is added in a regulated amount to the mixture to control the freezing temperature and to control the rate of freezing.
2. Description of the Prior Art
One prior method of freezing a batch amount of material to a low temperature involves placing the material in containers which are then suspended a short distance above the level of liquid nitrogen in a liquid nitrogen storage container. Due to the cold equilibrium temperature existing above the liquid nitrogen, the materials will slowly lower in temperature until frozen and further subcooling has taken place. A disadvantage of this process, however, is that it takes a considerable amount of time for the materials to be frozen and there is a lower survival rate of product.
Another technique to freeze materials to subfreezing temperatures is to place the materials in containers and to then submerge the containers directly into liquid nitrogen. The disadvantage of this technique relates to the inability for some biological materials which contain water to withstand the very rapid rate of freezing which takes place when the materials are immersed in the extremely cold liquid nitrogen.
3. Objects of the Invention
It is an object of this invention to be able to cool batch quantities of materials in a rapid manner to very low sub-freezing temperatures.
It is another object of this invention to be able to freeze batch quantities of materials under accurately controlled temperature conditions so as to control the rate of cooling.
It is a further object of the invention to have a batch freezing apparatus with a controlled amount of a cooling gas circulating through the freezing chamber. The temperature and freezing rate is regulated by the addition to the circulating gas of a controlled amount of a cold gas.
It is another object of the invention to have a batch freezing apparatus with a freezing chamber capable of rotation so the material being frozen in cylinderical containers is rotated against the inner surface of the wall of the container during the freezing process.
These and other objects of the invention will become apparent as the description of this invention proceeds.